Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art, exhaust a complex mixture of air pollutants. These air pollutants may be composed of gaseous compounds such as, for example, the oxides of nitrogen (NOx).
To reduce NOx content in the exhaust gas discharged to atmosphere, a NOx reduction system is utilized. In a conventional NOx reduction system, a reducing agent is introduced into the exhaust gas stream in the presence of a catalyst to remove NOx compounds from the exhaust gases. Some examples of reducing agents for reducing NOx compounds include ammonia, certain ammonium compounds, or urea.
The reducing agent may be introduced into the exhaust gas by an injector of a distribution system. The injector receives the reducing agent from a storage tank via a supply line. When the engine is shutdown, some of the reducing agent may freeze in various components such as the injector, the supply line, etc. of the distribution system. The freezing of the reducing agent may cause bulging or even rupture of the supply conduit. Further, due to frozen reducing agent, the injector may not efficiently deliver the reducing agent to the exhaust gas when the engine is operated again, which is not desirable.
One way of preventing the freezing of the reducing agent in various components of the distribution system is to purge the reducing agent from the injector, the supply line and any other component of the distribution system when the engine is shutdown. The distribution system may operate a pump for performing the purge. As the purge duration depends on the length of the supply line, the purge duration may be different for different engines or engine applications. Therefore, engines may have different purge calibrations for performing effective purging of the distribution system.
Alternatively, there may be a single purge calibration for all engines or engine applications. The single purge calibration may be developed based on the engine having the longest length of the supply line. Thereby, the purging for all engines is performed for the maximum time duration equivalent to the engine having the longest length of the supply line. This may cause excess idle time for the engine and/or machine, and its operator, which is not desirable. Further, the pump may operate even after complete removal of the reducing agent from the distribution system. In this scenario, cavitation may occur, thereby reducing life of the pump.
FR Patent No. 2,981,689 discloses a method and system for injecting liquid reagent into exhaust line of an engine for reducing oxides of nitrogen in the exhaust gas. The patent further describes method for purging the system of injecting liquid reagent. The method discloses determining completion of the purge event based on a pressure value in a liquid reagent supply line.